Wood construction is experiencing a new youth thanks to the technical development of some derived products. This includes laminated beams, also called laminated or laminated wood. They offer a number of benefits that improve those offered by other traditional materials within the building.
Among the uses of laminated beams, the construction of all types of structures is the most prominent. It is used both to make pergolas or porches, heavy wooden houses or large structures such as convention centers, industrial buildings or sports complexes. it is great dimensional stability and resistance make them ideal for building complex shapes, not just straight, but also curved.
Laminated wooden beams are essentially several slats glued to horizontal sections. At least four pieces are used, always with the grain in the longitudinal direction, to form a laminated beam. It is common, from a linguistic point of view, to confuse laminated beams with counter-laminated panels, which although they follow the same principle, from the point of view of wooden construction they have different uses.
The Manufacturing Process
The wood is previously selected. Defective slabs that can decrease beam stability are discarded. Sometimes, when the beam will become visible, parts with aesthetic defects are also discarded.
The manufacturing process for laminated beams goes through several phases: wood drying, selection, brushing, application of glues and adhesives, pressing, final brushing and sanding.
The drying it is a fundamental step. If the wood is not done correctly, already in place, it can reduce what, in addition to generating cracks in the wood itself, can affect the stability of the structure. To give you an idea, there may be a loss between 10 mm and 20 mm in a 24 cm beam when going from a humidity level of 30% to 10%. Drying is considered optimal when the wood reaches 12% humidity.
The most used woods for its manufacture are fir and wild pine. Although we can also find other species of pine, larch, chestnut, eucalyptus, beech, oak or iroko among others.
It is common to sell glued laminated beams, in addition to their dimensions or type of wood, depending on whether they will be seen or not. That is, brushed, sanded and even treated. Basically, it will depend on whether they are hidden or hidden from view.
Features of laminated beams
- High load capacity.
- Dimensional stability. Wood normally contracts and expands with environmental and thermal changes. Laminated wood is treated so that these changes are kept to a minimum and do not affect the structure. Compared to sawn wood, laminated wood is much more stable.
- Reduced weight Compared to steel, this type of beam allows greater distances with much lower weights.
- Wide variety of lengths and thicknesses. It is available in lengths and thicknesses far superior to those of solid wood. For example, a glued laminated timber beam can reach 30 meters, while solid wood usually does not exceed 13. Although these lengths are possible, it is usually sold in smaller sizes, the most common being 12 meters long and 160 × 80 mm thick.
- Resistance to moisture. The previously dried and treated wood allows good resistance to moisture, even in adverse situations.
- Good fire resistance. Its consumption occurs at a constant speed, so it is relatively easy to calculate the time that a fire would take to deteriorate the structure. And that time is much longer than you think.
- Much lower environmental impact than steel or concrete alternatives. Wood is a natural and 100% renewable material.
- The possibility of manufacturing in the workshop allows the beams to reach the installation site without calculation errors and in the desired shapes. Which reduces contingencies and expenses.
Regulations and standardization
Laminated wood is a product that must undergo a rigorous manufacturing and control process in order to facilitate and ensure calculations and safety for use in wooden structures.
In this sense, the UNE-EN 14080 “Wooden structures. Glued laminated wood and glued solid wood. Requirements”Classifies wood in 8 strength classes:
- 4 of homogeneous composition (the leaves are of the same strength class as lumber): GL24h, GL28h, GL 32h and GL36h.
- 4 of mixed composition (the leaves at the top and bottom edges of the cross section are of a higher strength class): GL24c, GL28c, GL 32h and GL36c.
|Strong grade of laminated wood||GL24h||GL36h|
|Flexural strength||24 N / mm2||36 N / mm2|
|Tensile strength parallel to fiber||16.5 N / mm2||26 N / mm2|
|Elastic modulus parallel to the fiber (average value)||11,600||14,700|
From a commercial point of view, the beams that we are likely to encounter GL24h and GL28h, the rest are unusual.